The following discussion of the background to the invention is intended to facilitate an understanding of the invention. However, it should be appreciated that the discussion is not an acknowledgement or admission that any of the material referred to was published, known or part of the common general knowledge as at the priority date of the application.
Short nanofibres can be created by injecting a body-forming fluid, such as a polymer solution dissolved in water (0.1 to 30% wt/vol of solvent), into a dispersion medium, typically a fluid such as butanol or water, having a viscosity in the range of from about 1 to 100 centiPoise (cP) and moving at 0.1 to 10 m/s. Under these conditions, the polymer solution is drawn out and fractures into short fibres, while the rapid extraction of water from the polymer solution caused by the Butanol causes the polymer to gel. Fibre size can be controlled by varying the shear force and the polymer concentration, from 15 to 2500 nm diameter and 2 to 20 μm length.
One example of this nanofibre generation method is described in international patent application PCT/AU2012/001273, the contents of which are taken to be incorporated into this specification by this reference. This patent application describes a bench scale experimental apparatus for performing the described short nanofibre generation method. The apparatus consists of a rotary mixer having a 5 cm impeller blade immersed in a beaker of the dispersion medium (Butanol). The blade is surrounded by a metal ring which includes and is divided by a series of 16 circumferentially spaced apart slits having an area of 1.5 cm2. For fibre generation, the impeller of the mixer is driven to the required rotation (and thus shear rate) of between 4000 and 10000 rpm, providing a maximum velocity of the tip of the blade of around 26 m/s when at 10000 rpm. The selected body-forming fluid is then injected into the dispersion medium in the beaker through a 25 g needle adjacent to one of the ports on the side of the mixer in close proximity to the blade.
The impeller blade configuration and rotation speed of this bench scale experimental apparatus provides a non-laminar (turbulent) system within the solvent. This creates significant mixing within the solvent, and thus poor predictability and control over the reagents within the system. Moreover, the overall system configuration provides poor control over rate of polymer injection, and poor control over the positioning of the needle tip.
Mercader et al. (2010) Kinetics of fibre solidification, PNAS early edition, (www.pnas.org/cgi/doi/10.1073/pnas.1003302107) describes an experimental apparatus for investigating the kinetics of fibre solidification comprising a capillary pipe with a diameter constriction. The diameter constriction of the pipe was used to produce an extensional flow a coflowing stream of an aqueous PVA solution. Nanofibres were produced by injecting an aqueous dispersion of nanotubes into the coflowing PVA stream upstream of the constriction. The injected nanotubes underwent bridging coagulation when contacted with the PVA solution to form a fibre. The fibre was translated and extended by the surrounding fluid at the center of the pipe at a controlled velocity. The constriction was shown to produce a net tensile stress in the fibre in response to viscous drag. The formed fibre was also shown to fragment into shorter length fibres when the surrounding drag forces exceed the tensile strength of the fibre.
While fibres and short fibres are shown to be produced by this method, it is considered that the described apparatus does not provide sufficient control of the reagents and flow conditions for the reproducible production of fibres of small diameter. Moreover, as described, there is anticipated to be some difficulties in alignment of the injection port with the centre of the capillary.
It would therefore be desirable to provide an improved and/or alternative device for the production of drawn bodies such as fibres, preferably short nano-fibres.